For timer, there are 2 types. With memory (backup battery) or without. With battery a good brand like Hager will have 2 days backup battery. The backup battery allows when there is a electrical disruption for the timer to recall the actual time. Cost around RM85. The cheaper timer without backup battery will not continue after electrical disruption and needs to be manually setup again the clock. Cost around RM50.

For such timer, unless you know what you are doing, you need an electrician.